This is what I do in regards the rear roller bearing, I do not believe there is a standard bearing available (metric bore, imperial outside diameter). I buy good quality sealed 6202 bearings with a 16mm bore (6202 are available in 15mm,16mm and 5/8" bores), I machine a steel sleeve with the correct od and lightly press/loctite it on to the bearing.
It then fits straight in to the standard pressed housings, the rear roller spins really nicely.
